1. Field of the Invention
The present invention relates to an apparatus for reading recorded information from a recording medium (for example, an optical disk) having a track for recording information.
2. Description of the Related Art
Optical disks such as laser vision disks have so-called track structures. In such a track structure, signals are recorded by forming a train of signal pits spirally from inner circumference to outer circumference of the optical disk. However, optical disks having the track structures encounter the problem of crosstalk in which the signal read from a track which is being traced contains the signals recorded on adjacent tracks. It is pointed out that the crosstalk is caused by the fact that a reading laser beam illuminates not only the track to be traced but also the adjacent tracks due to the relation between the spot diameter of the laser beam and the interval between adjacent tracks. As a result, the signals recorded on the tracks adjacent to the traced track are also read together with the signal recorded on the desired track.
To prevent such crosstalk, for example, two methods are known. The first method includes the steps of detecting the inclination of an optical pickup and correcting the position of the optical pickup so that it always correctly opposes the recording surface of an optical disk. The second method includes the steps of simultaneously read three adjacent tracks and performing subtraction using them.
The first method utilizes an arrangement in which a light emitted from a light emitting element and reflected by the optical disk, is received by two light receiving elements disposed adjacent to the light emitting element on opposite sides thereof. In the first method, the signal levels output from the respective light receiving elements are compared with each other by a differential amplifier to detect the inclination of the optical disk, thereby correcting the positions of the light emitting element and the light receiving elements with respect to the surface of the optical disk in accordance with the degree of inclination thereof. However, the first method has a number of problems. For example, a pickup having an excessively large size is needed because such an arrangement for detecting the inclination of the disk is provided independently of a device for reading information on the disk. Further, a part of the emitted light may not accurately fall on the optical disk in the outer circumferential portion thereof, with the result that no correct value is output.
The second method is disclosed in, for example, Japanese Patent Laid-Open No. 57/5824. The second method includes the steps of simultaneously reading three adjacent tracks and performing subtraction using the readout value. However, the second method still has a number of problems. A complicated pickup is needed, and since the signals read from adjacent tracks contain the same amount of crosstalk, it is only possible to improve recording density to such an extent that the crosstalk can be ignored.